PROCESSING OF ANTIMONY ORES

METALLURGY

The mineral dressing of sulfide ores is primarily accomplished by flotation although it can be accomplished by gravity and hand -sort methods. Recoveries of unoxidized sulfides (stibnite) can be in the mid 90% range with concentrate grades of 60 to 68%. The stibnite concentrates are then fumed to a crude oxide that is either refumed to a finished oxide or reduced to metal and then refumed to finished oxide. Tetrahedrite concentrates are usually leached in hot alkaline solutions that are electro-won to recover antimony metal or oxidized to sodium antimonite. Jamesonite concentrates are generally reduced to antimony-lead bullion (generally 50%-50%) that is selectively fumed to recover a crude oxide that is then reduced to metal and refumed to finished oxide. Alternatively, the antimony is drossed off the lead as sodium antimonate via the Harris process. Antimony may also be removed from lead bullion by selective crystallization by regulating the temperature so that it is above the melting point of lead, but below the melting point of antimony – a process developed by Asarco. Oxide ores are upgraded by gravity methods including jigs, tables, and heavy media separators (HMS plants). The mineral dressing of oxide ores generally result in recoveries of less than 50% and concentrate grades in the 25 to 40% antimony range at best. These concentrates are typically reduced directly to metal or fumed to crude oxide that is then refumed to finished oxide. In either case, the cost of reduction or initial fuming requires massive amounts of fuel and results in very high costs.

In summary, stibnite ores are the most desirable due to high recoveries and lower costs of conversion. Oxide ores are least desirable due to poor recoveries and the high cost of conversion.